Neuroanatomy 3 - Cerebellum and basal ganglia Flashcards
What is the function of the cerebellum ?
it receives information from the sensory systems; the spinal cord& other parts of the brain, it then regulates motor movements. It co-ordinates voluntary movements such as posture, balance, co-ordination & speech, resulting in smooth muscular activity
What are the 3 lobes of the cerebellum ?
- Anterior lobe
- Posterior lobe
- Floccularnodular lobe
What connects the cerebellum to the pons, midbrain and medulla?
3 stalks called the peduncles:
- Superior penduncle
- Medial penduncle
- Inferior penduncle
When looking at the histology of the cerebellum what does it consist of ?
- A tree-like structure called the ‘Abor vitae’ (tree of life) - white mater
- Has deep cerebellar nuclei (deep grey mater)
- Also has cerebellar cortex
What structure divides the cerebellum and what does it divide the cerebellum into ? (hint this is similar to the cerebrum)
The cerebellum is divided into a R and L hemisphere by the vermis
What is the function of each of the 3 peduncles and where does each of them connect to the brainstem ?
Superior peduncle - connects the cerebellum to the midbrain. It conveys signals mainly from the cerebellum to the cerebrum so mainly efferent nerve fibres
Middle peduncle - connects the cerebellum to the pons, it conveys impulses of voluntary movements from the cerebrum to the cerebellum (afferent fibres)
Inferior peduncle - connects cerebellum to the medulla, it carrys incoming vestibular & proprioceptive sensory fibres & outgoing motor fibres. Essentially receives info from joints & muscles and vestibular fibres, interprets them & then also sends out signals for co-ordinated movement together with the cerebrum
Appreciate this point:
The cerebrum is the thing which sends out the motor signals, the cerebellum asists with co-ordination & interpreting the best possible way to send out the motor signal being sent by the cerebrum (almost a bit like a proof reader)
What are the 3 layers of the cerebellar cortex ?
- Molecular layer (outer)
- purkinjie cell layer (middle)
- Granule cell layer (inner)
Describe the main route of afferent projections to the cerebellum (input)
Note afferent neurons = sensory neurons that carry nerve impulses from sensory stimuli towards CNS & brain
- Afferent fibres mainly arrive from the spinal cord, somatic proprioceptors & pressure receptors, the cerebral cortex via the pons & the vestibular apparatus via the vestibular nuceli
- These afferents enter via cerebellar peduncles & project mainly to the granular cell layer of the cerebellar cortex
Describe the main route of efferent projections of the cerebellum (output from the cerebellum)
Note - Efferent neurons = motor neurons that carry impulses away from the CNS & towards muscles to cause movement
- From all 3 lobes of the cerebellum, the only output is via the axons of purkinjie cells which mainly synapse on neurons of the deep cerebellar nuceli (deep grey mater) & subsequently contribute to coordinating the functions of all the motor tracts of the brainstem & spinal cord e.g. corticospinal, vestibulospinal tracts etc
- Most efferent axons of the deep cerebellar nuclei cross the midline & synapse in the thalamus. The thalamus then sends fibres to the motor cortex
Give an overview of the role of the cerebellum in the human body
- Cerebral cortex sends motor signals to the brainstem or spinal cord
- Signals can then be send to form a movement
- For coordinated movement the cerebellum must assist, before cerebral cortex can send signal out for co-ordinated movement the spinal cord & bainstem will send signals to cerebellum to tell it the position of muscles and joints so that the cerebellum can then make a blueprint for co-ordinated movement which it then sends to the thalamus and then to the cerebral cortex which then sends out signal for co-ordinated motor signal
Which side of the body do each of the cerebellar hemispheres influence ?
They influence the ipsilateral side of the body ==> lesions in one hemisphere lead to ipsilateral signs and symptoms (this is in contrast to lesions in the motor or sensory cortex which cause contralateral signs)
What signs does a unilateral cerebellar lesion result in ?
Disturbance of coordination in limbs. Can result in intention tremor and unsteady gait in the absence of weakness or sensory loss.
(believe the distrubance would be unilateral)
What signs does bilateral in the cerebellar dysfunction result in ?
Results in slowed, slurred speech (dysarthria) (believe this is because co-ordinated movement is required to produce speech), bilateral incoordination of the arms and a staggering, wide based gait (cerebellar ataxia).
Acute alcohol exposure typically results in bilateral cerebellar hemisphere dysfunction and presents with cerebellar ataxia. - so basically think of someone who is drunk
What signs do midline lesions in the cerebellum result in ?
Midline lesion: Disturbance of postural control. Patient will tend to fall over when standing or sitting despite preserved limb coordination.
What are the main basal ganglia?
- Caudate nucleus
- Putamen
- Globus pallidus
- Subthalamic nucleus
- Substantia nigra
Caudate nucleus and putamen is collectively known as the striatum
Putamen and the globus pallidus is collectively known as the lenticular nucleus
The caudate nucleus, putamen and globus pallidus is collectively known as the corpus striatum
Where is the substantia nigra located ?
Located in the midbrain
Go over the direct pathway of the basal ganglia
Essentially just know this point - Direct Pathway Enhances outflow of thalamus, enhancing the desired movement
Go over the indirect pathway of the basal ganglia
Essentially just know this; Indirect pathway - Inhibits outflow of thalamus
